Method and apparatus for fertigation with wastewater

ABSTRACT

Disclosed are methods and apparatus for blending wastewater with fresh water for fertigation of a crop. In one embodiment, the wastewater and the fresh water are blended at a predetermined flow ratio through a blending valve to obtain a blended stream. A logic based controller controls the blending valve to set a predetermined flow ratio according to the electricity conductivity (EC) of the blended water stream. The blending, measuring, and adjusting steps form a feedback loop so as to maintain the blended stream at a target EC value.

FIELD OF INVENTION

This invention relates to methods and apparatus for fertigation withwastewater, and more specifically to methods and apparatus forcontrolled blending of nutrient-rich wastewater with fresh water forpurposes of fertigation in connection with agricultural crops through adrip irrigation system.

BACKGROUND

Mountain snow packs and surface water are two main sources foragricultural water needs. Despite the possibility that farmland forcrops like cotton, cantaloupes, broccoli, and garlic may be fallow indrought years, empty fields are not an option for crops like silagecorn, which are main herd nutrition for dairies.

General strategies for coping with limited water include deficitirrigation of crops, improved irrigation efficiency and/or uniformity,improved crop genetics to develop varieties more tolerant to waterstress, and change of crop species. For example, some dairy producersmay forego planting silage corn, but instead choose to produce sorghum,which requires only two to three irrigations compared to corn's five toeight. The downside, however, is that use of sorghum could lead toreduced milk production.

An alternative strategy is the utilization of drip irrigation technologyto produce dairy crops. For example, a few innovative dairy producerslike DeJager farms have successfully produced silage corn with a dripirrigation system using synthetic fertilizers. A major constraint whichdeters the dairy industry's rapid transition to drip irrigation systemsis that the use of synthetic fertilizers displaces dairy manure, themain source of nutrients for forage.

In addition to being a nutrient resource, dairy manure presents animportant environmental challenge. Of particular concern is nitrogenpollution resulting from dairy manure applied via flood irrigation—oneof the major sources of groundwater contamination in California. Theproblem is particularly acute in the San Joaquin Valley where the vastmajority of the state's dairies reside, and where the long-termapplication of cow manure to crops has resulted in extensive groundwaterdegradation. San Joaquin Valley dairies are currently regulated under ageneral order issued in 2007 by the Central Valley Regional WaterQuality Control Board which requires nutrients to be applied atagronomic rates. This presents a difficult challenge since existingflood irrigation methods were practiced over roughly 450,000.00 acres in2015.

It is therefore desirable to have a technology that would enable theutilization of nutrients like liquid manure in drip irrigation systemswith increased water use efficiency to address drought, and at the sametime mitigate environmental challenges presented in managing theapplication of nutrients to fields. It is particularly desirable to havea technology that is able to maintain appropriate levels of nutrientsobtained from wastewater blended with a second source of water on acontinuous basis, automatically, without manual control or intervention.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a method for blending wastewaterwith fresh water for fertigation of a crop. In one embodiment, themethod comprises the steps of (a) providing a source of wastewater, saidwastewater containing nitrogen; (b) providing a source of fresh water;(c) blending the wastewater with the fresh water at a predetermined flowratio through a blending valve to obtain a blended water stream, whereina logic based irrigation controller controls the blending valve to setthe predetermined flow ratio; (d) measuring the electricity conductivity(EC) of the blended water stream with an EC sensor to obtain a measuredEC value; (e) adjusting the predetermined flow ratio by the logic basedirrigation controller according to the measured EC value; and (f)repeating steps c, d and e, as needed, until the measured EC value inthe blended water stream reaches a target EC value.

In another embodiment, the method comprises the steps of (a) providing asource of wastewater, said wastewater containing nitrogen; (b) providinga source of fresh water, said source of fresh water having anunrestricted or uncontrolled flow rate; (c) blending the wastewater withthe fresh water, wherein a logic based irrigation controller controls awastewater control valve to adjust the wastewater flow rate; (d)measuring the electricity conductivity (EC) of the blended water streamwith an EC sensor to obtain a measured EC value; (e) adjusting thewastewater flow rate by the logic based controller according to themeasured EC value; and (f) repeating steps c, d and e, as needed, untilthe measured EC value in the blended water stream reaches a target ECvalue.

In a further embodiment, the method comprises (a) providing a source ofwastewater, said wastewater containing nitrogen and said source ofwastewater independently controlled by a first variable speed pump; (b)providing a source of fresh water, said source of fresh waterindependently controlled by a second variable speed pump; (c) blendingthe wastewater with the fresh water to obtain a blended water stream,wherein a logic based irrigation controller controls a variablefrequency drive (VFD) motor control for the first and second variablespeed pumps; (d) measuring the electricity conductivity (EC) of theblended water stream with an EC sensor to obtain a measured EC value;(e) adjusting the wastewater and fresh water flow rates by the logicbased controller according to the measured EC value; and (f) repeatingsteps c, d and e, as needed, until the measured EC value in the blendedwater stream reaches a target EC value.

In further embodiments, the methods may comprise a step of feeding theblended water stream in step (f) through an irrigation system. Thatirrigation system may be a drip irrigation system, and in one preferredembodiment, the drip irrigation system may be a sub-surface irrigationsystem. In certain embodiments, particularly where there is the prospectof clogging the system, the blended water stream is filtered beforebeing fed though an irrigation system. A back-flush filter may be usedto the system to allow the filter to be cleared periodically.

The source of wastewater may be a farm storage lagoon. In otherembodiments, the source of fresh water is a well, surface stream, orfresh water reservoir. The blended water may be used, for example, forfertigation in a silage corn crop or a winter forage crop or othercrops. In some embodiments, the blending valve is a hydraulic blendingvalve or an electronically operated blending valve or a pneumaticallyoperated valve. In some embodiments, three or more sources of water maybe blended through the blending valve.

Additional blending methods involve, for example, unrestricted oruncontrolled fresh water inlet flow and controlled wastewater flow. Inone embodiment, one or more valves, which may be, but are not limitedto, mechanical, pneumatic, or hydraulic valves, control the wastewaterflow rate by opening or closing. Opening and closing of the valves ofthe present invention occur in response to EC measurements taken from anEC sensor that are implemented by one or more logic based controllers.

Further blending methods involve, for example, independently controlledfresh water and wastewater pumps, including, for example, variable speedpumps, that can change the flow rate of fresh water and wastewater,respectively, through one or more logic based controllers.

In some embodiments, the steps in the method are automated in acontinuous manner to maintain the measured EC value in the blended waterstream at a target EC value. In one embodiment, the target EC value maybe calculated according to the projected weekly nitrogen uptake and cropevapotranspiration (ETc) of a crop field. The calculation in aparticular instance may be based on the formula EC=0.0146÷0.227×uptake(lb Nitrogen/acre)÷ETc (inches)+0.3255.

Another aspect of the present invention is an apparatus for blendingwastewater with fresh water for fertigation of a crop. In a preferredembodiment, the apparatus comprises either (1) a blending valve forblending two or more sources of water into a blended water stream at apredetermined flow ratio, wherein the two or more sources of watercomprises at least one source of wastewater that contains nitrogen andat least one source of fresh water, (2) a wastewater control valve foradjusting the wastewater flow rate into a blended water stream, or (3) aVFD motor control for independently controlling a first variable speedpump connected to a wastewater source and a second variable speed pumpconnected to a fresh water source; an EC sensor for measuring theelectricity conductivity (EC) of the blended water stream; and a logicbased controller for controlling the blending valve/wastewater controlvalve/VFD motor control to set the predetermined flow ratio/wastewaterflow rate/fresh water flow rate according to the measured EC in theblended water stream. In some embodiments, the blending valve is ahydraulic blending valve or an electronically operated blending valve orpneumatic operated valve and in some, the logic based controllercomprises a motor actuator that actuates the flow ratio of the two ormore sources of water.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures. It isintended that the embodiments and figures disclosed herein are to beconsidered illustrative, rather than restrictive. The disclosure,however, both as to organization and method of operation, together withobjects, features, and advantages thereof, may best be understood byreference to the following detailed description when read with theaccompanying figures, in which:

FIG. 1 shows a flow chart depicting the steps for blending wastewaterwith fresh water in a controlled manner.

FIG. 2 shows a sketch depicting components of an apparatus for blendingwastewater with fresh water in a controlled manner.

FIG. 3 shows a graph depicting the linear regression of EC_(w) andnitrogen concentration in water.

FIG. 4 shows a flow chart depicting the steps for blending wastewaterwith fresh water wherein the fresh water inlet flow is unrestricted oruncontrolled and the wastewater flow rate is controlled by one or morewastewater control valves.

FIG. 5 shows a flow chart depicting the steps for blending wastewaterwith fresh water wherein the fresh water and wastewater flow rates arecontrolled independently by pumps that can change the flow rate of bothfresh water and wastewater based on one or more logic-based controllers.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated within the figures toindicate like elements.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have designed methods for blending wastewater with freshwater to apply nutrients to crops in a controlled manner, and severalapparatus for practicing the method. The inventions are in part based onthe establishment of a proxy relationship between electricityconductivity (EC) value and nitrogen content in water.

Methods

A principal aspect of the invention is a method for blending wastewaterwith fresh water to make a blended stream for use in targeting cropswith an application of nutrients. As shown in FIG. 1, the method is anautomated method in which the steps in the method are performed in acontinuous manner. This may include the steps of providing a source ofwastewater 1, said wastewater containing nitrogen; providing a source offresh water 2; blending the wastewater with the fresh water at apredetermined flow ratio through a blending valve 3 to obtain a blendedwater stream 4, wherein a logic based controller 6 controls the blendingvalve to set the predetermined flow ratio; measuring the electricityconductivity (EC) of the blended water stream with an EC sensor 5 toobtain a measured EC value; adjusting the predetermined flow ratio bythe logic based controller according to the measured EC value 11; andrepeating the above blending, measuring, and adjusting steps until themeasured EC value in the blended water stream reaches a target EC value.The logic based controller 6 receives a signal from the EC sensor 5 anddetermines whether a target EC has been reached in the blended waterstream. When a target EC has been reached 9, the logic based controllerwill not adjust the flow ratio in the blending valve 10. When a targetEC has not been reached 8, the logic based controller will automaticallyadjust the flow ratio in the blending valve by an actuator 11.

In contrast to the semi-automated method embodiments described below,the automated method embodiments may be applied even when the nutrientconcentrations in the wastewater 1 may vary with time. Additionally, inthe automated method embodiments, the adjustment of the predeterminedflow ratio 11 does not rely on the skill of the operator who would haveto set the predetermined flow ratio manually. Further, in the automatedmethod embodiments, there is no cost of lab analyses or any time delayin obtaining lab results. In the automated method embodiments of theinvention, the adjustments of flow ratios take place in real time andprovide improved precision.

In another embodiment, the method is a semi-automated method in whichsome of the aforementioned steps in the method, or additional steps, areperformed manually. For example, samples of the nutrient rich wastewatercould be taken manually every other week and delivered to a lab foranalysis. Once lab results are received, manual calculations can becompleted to determine the appropriate amounts of fresh and wastewaterto blend to obtain the targeted rates of nutrients to be applied to thecrop. As another example, the incoming flow ratios from the wastewaterand the natural sources could be adjusted using manual valves and visualreadings of flowmeters on both the fresh and wastewater sources. Oncethese values and valves were set, the system would operate in a staticposition until the next testing of the nutrient rich wastewater isperformed, ordinarily in 1-2 weeks. Semi-automated methods may beapplied when there are no constant changes in the nutrient levels of thewastewater, no significant changes in pressure conditions of the watersources, and/or the operator is well-trained to adjust the flow ratios.

In some embodiments, the blended stream that has attained the targetedEC level will be fed through an irrigation system immediately forfertigation on a crop. In other instances, a blended water stream thathas attained the targeted EC level is not immediately fed into anirrigation system but instead is filtered to exclude particles thatwould prevent an irrigation system from functioning properly. Thefiltration may be carried out using a commercially available filterknown in the art.

Another aspect of the invention is a method for blending wastewater withfresh water to make a blended stream for use in targeting crops with anapplication of nutrients. As shown in FIG. 4, the method is an automatedmethod in which the steps in the method are performed in a continuousmanner. This may include the steps of providing a source of wastewater1, said wastewater containing nitrogen, and wherein said wastewaterpasses through a wastewater control valve 3; providing a source of freshwater 2, wherein the source of fresh water is a full system orunrestricted flow of fresh water; blending the wastewater and freshwater to obtain a blended water stream 4, wherein a logic basedcontroller 6 controls the wastewater control valve to set the wastewaterflow rate; measuring the EC of the blended water stream with an ECsensor 5 to obtain a measured EC value; adjusting the wastewater flowrate by the logic based controller according to the measured EC value11; and repeating the above blending, measuring, and adjusting stepsuntil the measured EC value in the blended water stream reaches a targetEC value. The logic based controller 6 receives a signal from the ECsensor 5 and determines whether a target EC has been reached in theblended water stream. When a target EC has been reached 9, the logicbased controller will not adjust the flow in the wastewater controlvalve 10. When a target EC has not been reached 8, the logic basedcontroller will automatically adjust the flow ratio in the wastewatercontrol valve by an actuator 11.

Another aspect of the invention is a method for blending wastewater withfresh water to make a blended stream for use in targeting crops with anapplication of nutrients. As shown in FIG. 5, the method is an automatedmethod in which the steps in the method are performed in a continuousmanner. This may include the steps of providing a source of wastewater1, said wastewater containing nitrogen and originating from a sourceequipped with a variable speed drive pump motor; providing a source offresh water 2 that originates from a source equipped with a variablespeed drive pump motor; blending the wastewater and fresh water toobtain a blended water stream 4, wherein a logic based controller 6controls the VFD motor control 3 to set the wastewater and fresh waterflow rates; measuring the EC of the blended water stream with an ECsensor 5 to obtain a measured EC value; adjusting the wastewater flowrate and/or the fresh water flow rate by the logic based controlleraccording to the measured EC value 11; and repeating the above blending,measuring, and adjusting steps until the measured EC value in theblended water stream reaches a target EC value. The logic basedcontroller 6 receives a signal from the EC sensor 5 and determineswhether a target EC has been reached in the blended water stream. When atarget EC has been reached 9, the logic based controller will not adjustthe flow via the VFD Pump Motor 10. When a target EC has not beenreached 8, the logic based controller will automatically adjust the flowratio in the VFD pump motor by an actuator 11.

Examples of an irrigation system include a pipe network coupled withdrip emitters, emitting tape or sprinklers. The pipe may be a solid pipeor a flexible pipe. Examples of the pipes are described in U.S. Pat.Nos. 8,893,987 and 8,672,240. Examples of drip emitters are described inU.S. Pat. Nos. 8,511,585 and 7,410,108. In a certain embodiment, theirrigation system is a drip irrigation system such as the systemdescribed in U.S. Pat. No. 4,210,287. The method may be used forfertigation for any variety of crops and, preferably dairy crops, e.g.,silage corn and winter forage, in particular.

In some embodiments, the wastewater may be from any source including theliquid dairy manure from a storage lagoon or similar facilities. In someembodiments, the source of fresh water may be a well, a surface stream,river, slough canal or other surface water source or a fresh waterreservoir. Water from the various sources used may be pumped separatelyinto a blending valve. As shown in FIG. 2, the wastewater may be pumpedby a wastewater pump 12 into a pipe 14 that is connected to a blendingvalve 3, and the fresh water may be pumped by a fresh water pump 13 intoa pipe 16 that is connected to the same blending valve 3.

The flow ratio of each water source may be adjusted by adjusting theblending valve. For example, to increase nutrient level in the blendedwater stream, the opening in the blending valve towards the wastewaterpipe is expanded. In a certain embodiment, the adjustment is achieved bya motor actuator 11. A motor actuator may adjust the blending valveaccording to the measured EC value in the blended water stream and thetarget EC value. In one embodiment, a motor-operated valve that opensand closes the fresh water and/or wastewater feeds to varying degrees inresponse to feedback from the controller is used.

In some embodiments, the target EC value may be calculated according tothe relationship between EC and nitrogen content that has beenestablished. Example 1 provides a detailed example as to theestablishment of such a relationship as well as how to calculate thetarget EC value. The establishment of the relationship between EC valueand nitrogen content makes it feasible to automatically control nitrogenconcentration in a blended water stream by monitoring the EC value ofthe blended water stream. Without the herein established proxyrelationship between EC value and nitrogen content, one has toperiodically take water samples, often manually, from the blended waterstream and measure the nitrogen content in the water samples separatelyin a relatively much more time- and labor-intensive manner. The targetEC value is a function of the nitrogen demands of the particular cropbeing fertilized. Nitrogen demands for given crops are generally known.

In FIG. 1, steps/modules 3 to 11 form a feedback loop, which is runconstantly with the objective of maintaining a pre-determined level ofnutrients in the blended water to achieve the targeted level of nutrientapplication to crops. The method enables the utilization of wastewater,e.g., liquid manure, for fertigation in a drip irrigation system, whichresults in increased water use efficiency to address drought issues.Further, the method also mitigates environmental challenges in managingnutrients applied to the field because the amount of nutrient, e.g.,nitrogen, is precisely controlled.

Apparatus

Another aspect of the present invention is an apparatus for practicingthe methods of the present invention as set forth in, for example,FIG. 1. In one embodiment, the apparatus comprises a blending valve 3for blending two or more sources of water into a blended water stream 4at a predetermined flow ratio, wherein the two or more sources of watercomprise at least one source of wastewater 1 that contains nitrogen andat least one source of fresh water 2; an EC sensor 5 for measuring theelectricity conductivity (EC) of the blended water stream; and a logicbased controller 6 for controlling the blending valve to set thepredetermined flow ratio according to the measured EC in the blendedwater stream 7-11.

Another aspect of the present invention is an apparatus for practicingthe methods of the present invention as set forth in, for example, FIG.4. In one embodiment, the apparatus comprises a wastewater control valve3 for controlling the flow of wastewater into a blended water stream 4,wherein the two or more sources of water comprises at least one sourceof wastewater 1 that contains nitrogen and at least one source of freshwater 2, wherein the fresh water is a full system or unrestricted flowof fresh water; an EC sensor 5 for measuring the electricityconductivity (EC) of the blended water stream; and a logic basedcontroller 6 for controlling the wastewater control valve to adjust thewastewater flow according to the measured EC in the blended water stream7-11.

Another aspect of the present invention is an apparatus for practicingthe methods of the present invention as set forth in, for example, FIG.5. In one embodiment, the apparatus comprises a VFD Motor Control 3 forindependently controlling the flow of wastewater and fresh water, bothvia variable speed drive pump motors, into a blended water stream 4,wherein the two or more sources of water comprise at least one source ofwastewater 1 that contains nitrogen and at least one source of freshwater 2; an EC sensor 5 for measuring the electricity conductivity (EC)of the blended water stream; and a logic based controller 6 forcontrolling the VFD Motor Control to adjust the wastewater and freshwater flow according to the measured EC in the blended water stream7-11.

The blending valve 3 is preferably a hydraulic orelectronically-operated blending valve. For example, a Dorot blendingvalve, which is well-known in the art, may be used. The blending valvemay be used for regulating a fixed pre-set flow ratio between two ormore lines regardless of fluctuating pressures and changing demands.Alternatively, the flow ratio may be set by the user or allowed to vary.

Another blending apparatus has a fresh water inlet with an unrestrictedor uncontrolled flow and a wastewater inlet with a controlled flow. Theapparatus uses one or more valves, for example, mechanical, pneumatic,or hydraulic valves, that open or close depending on the desired flowrate determined by EC and implemented by a logic based controller.

Yet another blending apparatus utilizes variable speed drive pump motorscontrolled by a VFD motor control to blend fresh water and wastewaterfrom their respective sources. In this apparatus, wastewater and freshwater flow rates are independently controlled based on the logic basedcontroller.

In some embodiments, the EC sensor 5 may be any sensor that detectselectricity conductivity known in the art. In some embodiments, the ECsensor 5 is coupled to an EC transmitter. In other embodiments, the ECsensors and EC transmitters may also be pH sensors and pH transmitters.

In some embodiments, the logic based controller 6 may receive signalssent either through a wire or wirelessly from EC sensors. Controller 6typically processes the signal to determine whether an EC target isreached. In one embodiment, the logic based controller further comprisesan actuator that actuates the blending valve when an EC target is notreached.

One exemplary actuator is an ESBE series 90 electronic motor actuatorthat may rotate rotary valves. The actuator may be adjustedautomatically or manually. In a certain embodiment, the actuator mayactuate 2 sources of water in the blending valve. In another certainembodiment, the actuator may actuate 3 sources of water in the blendingvalve. In a further certain embodiment, the actuator may actuate 4sources of water in the blending valve.

Example 1

In this Example, the inventors first established a relationship betweenEC and nitrogen concentration in a blend of wastewater and well water.The inventors then utilized the method to make precisely targetedapplications of nitrogen through blended water using the NetafimFertiKit™ EC sensor and the Netafim NMC™ logical controller to controlthe blending valve.

TABLE 1 Chart Showing Sample Analysis Results ECw TKN NH₄—N NO₃—N N DateSource Lab FW/WW mmhos/cm ppm ppm ppm ppm May. 20, 2010 DW 16 Dellavalle0.35 2.5 2.5 Aug 10, 2011 DW 16 Dellavalle 0.38 3.8 3.8 Jul. 5, 2012 DW16 Dellavalle 0.40 4.5 4.5 Jul. 25, 2013 DW 16 Dellavalle 0.84 21.4 21.4Jun. 24, 2014 Lagoon Denele 5.97 538 409 538 Jun. 24, 2014 Lagoon Denele6.81 549 493 549 Jul. 29, 2014 Lagoon Denele 6.86 386 370 386 Jul. 30,2014 DW 16 Dellavalle 0.69 15.7 15.7 Aug. 1, 2014 Blend Denele 240/501.77 112 64 112 Aug. 5, 2014 Lagoon Denele 8.85 566 389 566 Aug. 5, 2014WW Denele 8.61 560 395 560 Aug. 5, 2014 Blend Denele 240/50 2.11 118 64118 Aug. 12, 2014 DW 16 Denele 0.70 16.2 16.2 Aug. 12, 2014 WW Denele8.35 510 445 510 Aug. 12, 2014 Blend Denele 240/50 2.26 118 81 118 Aug.19, 2014 WW Denele 8.45 554 468 554 Mar. 25, 2015 DW16 Denele 0.52 7.17.1 Mar. 25, 2015 WW Denele 13.5 812 560 812 Mar. 25, 2015 Blend Denele230/10 1.05 67 59 67

Methods: Wastewater, well water and field blends were sampledperiodically during the corn, wheat, and other forage crop growingseasons. Wastewater was collected (dipped) from the DeJager Northstorage lagoon and from the pressurized distribution line upstream ofthe mixing and filter station at the trial site. Well water was sampleddirectly from the DW 16 discharge and the field blends—wastewaterblended with well water—were sampled downstream of the filters asirrigation was in progress. Flow rates (from the system flowmeters) werenoted as blended samples were collected. All of the samples wereanalyzed for the target ECw (w refers to water), TKN (wastewater,including blends), NO3-N (well water), pH and other macro- andmicro-nutrients, at Denele Analytical Lab in Turlock. ECw and NO3-N fromDW 16 water analyses going back four years were also added to the dataset (Table 1).

Results: The measures of nitrogen in wastewater were Total KjeldahlNitrogen (TKN) and ammonium-N(NH4-N). TKN included NH4-N as well asorganic N, and while organic N had to be mineralized to beplant-available, it was reasonable to assume that Field 144, with ahistory of yearly manure applications—liquid and solid—was in a steadystate of organic nitrogen mineralization. Thus, it was reasonable hereto use TKN as a measure of plant-available nitrogen. TKN has also beenused by dairies to provide reports to the Water Board on appliednitrogen in wastewater.

By including ECw and nitrogen from all of the water analyses in the dataset and performing simple linear regression with N as the independentvariable, the inventors obtained the following relationship:ECw=0.0146×ppm N+0.3255R ²=0.9649(FIG. 3).

Converting from ppm N

${{ppm}\mspace{14mu} N \times 0.227} = \frac{{lb}\mspace{14mu} N}{{acre}*{inch}}$${ECw} = {\frac{0.0146}{0.227} = {{\frac{{lb}\mspace{14mu} N}{acre} \times \frac{1}{inch}} + {0.3255.}}}$

In this general form, an ECw target could be set using the projectedweekly N uptake and ETc:

${ECw} = {{\frac{0.0146}{0.227} \times {Uptake}\mspace{14mu}{( \frac{{lb}\mspace{14mu} N}{acre} ) \div {ETc}}\mspace{14mu}({inches})} + {0.3255.}}$

In one example, three 13-acre treatment blocks in Field 144 wereirrigated in 12-hour sets. To apply a target amount of N in a set time,the following calculation was run:

${ECw} = {\frac{0.0146}{0.227} \times {\quad{{{Uptake}\mspace{14mu}{( \frac{{lb}\mspace{14mu} N}{acre} ) \div {{\quad\quad}\lbrack {{{Precip}.\mspace{14mu}{rate}}\mspace{14mu}( \frac{inches}{hour} ) \times {Run}\mspace{14mu}{time}\mspace{14mu}({hours})} \rbrack}}} + {0.3255.}}}}$

The target ECw could then be entered in the NMC program which controlledthe blending valves. The resolution of the EC sensor in that instancewas 0.1 mmho/cm, or a concentration of 1.6 lb N/acre-inch.

We claim:
 1. A method for blending wastewater with fresh water forfertigation of a crop, comprising: (a) providing a source of wastewater,the wastewater containing nitrogen; (b) providing a source of freshwater, said source of fresh water having an unrestricted or uncontrolledflow rate; (c) blending the wastewater with the fresh water with asingle blending valve, wherein an irrigation controller controls awastewater control valve to adjust the wastewater flow rate; (d)measuring the electricity conductivity (EC) of the blended water streamwith an EC sensor to obtain a measured EC value, wherein the measured ECvalue is derived at least from the nitrogen content of the blended waterstream; (e) adjusting the wastewater flow rate by the irrigationcontroller according to the measured EC value; and (f) repeating steps(c), (d), and (e), as needed, until the measured EC value in the blendedwater stream reaches a target EC value.
 2. The method of claim 1,further comprising a step of feeding the blended water stream through anirrigation system following step (f).
 3. The method of claim 2, whereinthe irrigation system is a drip irrigation system.
 4. The method ofclaim 3, wherein the drip irrigation system is a sub-surface irrigationsystem.
 5. The method of claim 3, wherein the drip irrigation system isa surface irrigation system.
 6. The method of claim 2, wherein theblended water stream is filtered before being fed through an irrigationsystem.
 7. The method of claim 1, wherein the source of wastewater is afarm storage lagoon.
 8. The method of claim 1, wherein the source offresh water is a well, a surface stream, river, drainage slough, canal,pipeline or a fresh water reservoir.
 9. The method of claim 1, whereinthe crop is a silage corn crop.
 10. The method of claim 1, wherein thesteps c to f are automatically performed in a continuous manner tomaintain the measured EC value in the blended water stream at the targetEC value.
 11. The method of claim 1, wherein the target EC value iscalculated according to the projected weekly nitrogen uptake and cropevapotranspiration (ETc).
 12. The method of claim 11, wherein the targetEC value is calculated based on the formula EC=0.0146÷ 0.227×uptake (lbNitrogen/acre)÷ETc (inches)+0.3255.
 13. The method of claim 1, whereinthe nitrogen in the wastewater is derived from manure.
 14. The method ofclaim 1, wherein the target EC value is greater than zero and less thanabout 2.5 mmhos/cm.
 15. The method of claim 14, wherein the target ECvalue is greater than about 1 mmhos/cm and less than about 2.25mmhos/cm.
 16. The method of claim 1, wherein the nitrogen content of theblended water stream is greater than zero parts per million (ppm) andless than about 150 ppm.
 17. The method of claim 16, wherein thenitrogen content of the blended water stream is greater than about 50ppm and less than about 125 ppm.
 18. An apparatus for blendingwastewater with fresh water for fertigation of a crop, comprising: (a) asingle blending valve for blending wastewater with fresh water; (b) awastewater control valve for adjusting the wastewater flow rate into ablended water stream; (c) an EC sensor for measuring the electricityconductivity (EC) of the blended water stream, wherein the measured ECvalue is derived at least from nitrogen content of the blended waterstream; and (d) an irrigation controller for controlling the wastewatercontrol valve to set the wastewater flow rate according to the ECdetermined for the blended water stream.
 19. The apparatus of claim 18,wherein the wastewater control valve is a hydraulic wastewater controlvalve.
 20. The apparatus of claim 18, wherein the wastewater controlvalve is an electronically operated wastewater control valve.
 21. Theapparatus of claim 18, wherein the wastewater control valve is apneumatic wastewater control valve.
 22. The apparatus of claim 18,wherein the irrigation controller comprises a motor actuator thatactuates the flow rate of the wastewater and fresh water.
 23. Theapparatus of claim 18, wherein said EC sensor is able to continuouslymonitor the EC level and the irrigation controller controls thewastewater control valve to maintain the wastewater flow rateautomatically and continuously.
 24. The apparatus of claim 18, whereinthe nitrogen in the wastewater is derived from manure.
 25. The apparatusof claim 18, wherein the target EC value is greater than zero and lessthan about 2.5 mmhos/cm.
 26. The apparatus of claim 25, wherein thetarget EC value is greater than about 1 mmhos/cm and less than about2.25 mmhos/cm.
 27. The apparatus of claim 18, wherein the nitrogencontent of the blended water stream is greater than zero parts permillion (ppm) and less than about 150 ppm.
 28. The apparatus of claim27, wherein the nitrogen content of the blended water stream is greaterthan about 50 ppm and less than about 125 ppm.
 29. A method for blendingwastewater with fresh water for fertigation of a crop, comprising: (a)providing a source of wastewater, said wastewater containing nitrogenand said source of wastewater independently controlled by a firstvariable speed pump; (b) providing a source of fresh water, said sourceof fresh water independently controlled by a second variable speed pump;(c) blending the wastewater with the fresh water with a single blendingvalve to obtain a blended water stream, wherein an irrigation controllercontrols a variable frequency drive (VFD) motor control for the firstand second variable speed pumps; (d) measuring the electricityconductivity (EC) of the blended water stream with an EC sensor toobtain a measured EC value, wherein the measured EC value is derived atleast from the nitrogen content of the blended water stream; (e)adjusting the wastewater and fresh water flow rates by the irrigationcontroller according to the measured EC value; and (f) repeating steps(c), (d), and (e), as needed, until the measured EC value in the blendedwater stream reaches a target EC value.
 30. The method of claim 29,further comprising a step of feeding the blended water stream through anirrigation system following step (f).
 31. The method of claim 30,wherein the irrigation system is a drip irrigation system.
 32. Themethod of claim 31, wherein the drip irrigation system is a sub-surfaceirrigation system.
 33. The method of claim 31, wherein the dripirrigation system is a surface irrigation system.
 34. The method ofclaim 30, wherein the blended water stream is filtered before being fedthrough an irrigation system.
 35. The method of claim 29, wherein thesource of wastewater is a farm storage lagoon.
 36. The method of claim29, wherein the source of fresh water is a well, a surface stream,river, drainage slough, canal, pipeline or a fresh water reservoir. 37.The method of claim 29, wherein the crop is a silage corn crop.
 38. Themethod of claim 29, wherein the steps (c) to (f) are automaticallyperformed in a continuous manner to maintain the measured EC value inthe blended water stream at a target EC value.
 39. The method of claim29, wherein the target EC value is calculated according to the projectedweekly nitrogen uptake and crop evapotranspiration (ETc).
 40. The methodof claim 39, wherein, the calculation is based on the formulaEC=0.0146÷0.227×uptake (lb Nitrogen/acre)÷ETc (inches)+0.3255.
 41. Themethod of claim 29, wherein the nitrogen in the wastewater is derivedfrom manure.
 42. The method of claim 29, wherein the target EC value isgreater than zero and less than about 2.5 mmhos/cm.
 43. The method ofclaim 42, wherein the target EC value is greater than about 1 mmhos/cmand less than about 2.25 mmhos/cm.
 44. The method of claim 29, whereinthe nitrogen content of the blended water stream is greater than zeroparts per million (ppm) and less than about 150 ppm.
 45. The method ofclaim 44, wherein the nitrogen content of the blended water stream isgreater than about 50 ppm and less than about 125 ppm.
 46. An apparatusfor blending wastewater with fresh water for fertigation of a crop,comprising: (a) a single blending valve for blending wastewater withfresh water; (b) a variable frequency drive (VFD) motor control forindependently controlling a first variable speed pump connected to awastewater source and a second variable speed pump connected to a freshwater source, (c) an EC sensor for measuring the electricityconductivity (EC) of the blended water stream, wherein the EC of theblended water stream is derived at least from the nitrogen content ofthe blended water stream; and (d) an irrigation controller forcontrolling the VFD motor control to set the wastewater flow rate andfresh water flow rate according to the EC determined for the blendedwater stream.
 47. The apparatus of claim 46, wherein the irrigationcontroller comprises a motor actuator that actuates the flow ratio ofthe two or more sources of water.
 48. The apparatus of claim 46, whereinsaid EC sensor is able to continuously monitor the EC level and theirrigation controller controls the blending valve to maintain thepredetermined flow ratio automatically and continuously.
 49. Theapparatus of claim 46, wherein the nitrogen in the wastewater is derivedfrom manure.
 50. The apparatus of claim 46, wherein the target EC valueis greater than zero and less than about 2.5 mmhos/cm.
 51. The apparatusof claim 50, wherein the target EC value is greater than about 1mmhos/cm and less than about 2.25 mmhos/cm.
 52. The apparatus of claim46, wherein the nitrogen content of the blended water stream is greaterthan zero parts per million (ppm) and less than about 150 ppm.
 53. Theapparatus of claim 52, wherein the nitrogen content of the blended waterstream is greater than about 50 ppm and less than about 125 ppm.
 54. Asub-surface apparatus for blending liquid manure with fresh water forfertigation of a crop, comprising: (a) a single blending valve forblending liquid manure with fresh water; (b) single blending valve forblending wastewater with fresh water; a wastewater control valve foradjusting the flow rate of wastewater into a blended water stream,wherein the wastewater is derived from liquid manure; (c) an EC sensorfor measuring the electricity conductivity (EC) of the blended waterstream, wherein the measured EC value is derived at least from nitrogencontent of the blended water stream; and (d) an irrigation controllerfor controlling the wastewater control valve to set the liquid manureflow rate according to the EC determined for the blended water stream.